You can design one primer in insertion sequence and another outside and use (separately) in pair with common single primer (if you know the insertion sequence).
Can also design flanking primers and sequence nucleotide content.
If insertion is large enough you can compare bands in gel electrophoresis and see size difference.
You can design one gene specific primer and another random primer and then sequence the amplicon obtained. The sequencing results obtained is then used to see where the insertion of gene is happened by doing the blast.